Three stack hybrid white oled for enhanced efficiency and lifetime

ABSTRACT

OLEDs containing a stacked hybrid architecture including a phosphorescent organic emissive unit and two fluorescent organic emissive units are disclosed. The stacked hybrid architecture includes a plurality of electrodes and a hybrid emissive stacked disposed between at least two of the electrodes. The stack contains at least three emissive units and at least two charge generation layers. At least one of the three emissive units is a phosphorescent organic emissive unit and at least two of the three emissive units are fluorescent organic emissive units. More specifically, the two fluorescent organic emissive units may be blue organic emissive units that emit light from the same or different color regions.

PRIORITY

This application is a continuation of Ser. No. 15/401,258, filed Jan. 9,2017, which is a continuation of U.S. Non-Provisional application Ser.No. 13/964,549, filed Aug. 12, 2013, which claims the benefit of U.S.Provisional Application No. 61/705,687, filed Sep. 26, 2012, thedisclosure of each of which is incorporated by reference in itsentirety.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to light emitting devices and, morespecifically, to fabricating OLEDs containing a stacked hybridarchitecture including a phosphorescent organic emissive unit and twofluorescent organic emissive units.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)3, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

According to aspects of the disclosed subject matter, a stacked hybridarchitecture is provided that includes a first electrode and a secondelectrode. A hybrid emissive stack is disposed between the firstelectrode and the second electrode and includes at least three emissiveunits and at least two charge generation layers. A first emissive unitof the three emissive units is disposed over the first electrode and afirst charge generation layer of the two charge generation layers isdisposed over the first emissive unit. A second emissive unit of thethree emissive units is disposed over the first charge generation layerand a second charge generation layer of the two charge generation layersis disposed over the second emissive unit. A third emissive unit of thethree emissive units is disposed over the second charge generationlayer. At least one of the three emissive units is a phosphorescentorganic emissive unit and at least two of the three emissive units arefluorescent organic emissive units. The phosphorescent organic emissiveunit may be a red, green, or yellow organic emissive unit (i.e., containa red, green, or yellow organic emissive layer) or may contain acombination of two or more colors. The at least two fluorescent organicemissive units may be blue organic emissive units, and may emit the sameblue light or different blue lights. A blocking layer may be disposedbetween the third emissive layer and the second electrode and, morespecifically, may be disposed between a phosphorescent organic emissivelayer and the second electrode. Alternatively or in addition, theblocking layer may be disposed between a phosphorescent organic emissivelayer and the first electrode. The first, second, or third emissive unitmay be the at least one phosphorescent organic emissive unit. Notably,implementations of the disclosed subject matter may enable any order ofdepositing the two fluorescent and one phosphorescent layer.Additionally, the stacked hybrid architecture may include a colorfilter.

According to aspects of the disclosed subject matter, a stacked hybriddevice may include a first electrode, a fluorescent blue organic firstemissive layer disposed over the first electrode, a first chargegeneration layer disposed over the organic first emissive layer, afluorescent blue second organic emissive layer organic emissive layerdisposed over the first charge generation layer, and a second chargegeneration layer disposed over the fluorescent blue second organicemissive layer. Additionally, the device may include an organic thirdemissive layer disposed over the second charge generation layer and asecond electrode disposed over the organic third emissive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example organic light emitting device.

FIG. 2 shows an example inverted organic light emitting device that doesnot have a separate electron transport layer.

FIG. 3a shows an example hybrid stack according to an implementation ofthe disclosed subject matter.

FIG. 3b shows another example hybrid stack according to animplementation of the disclosed subject matter.

FIG. 3c shows another example hybrid stack according to animplementation of the disclosed subject matter.

FIG. 4 shows another example hybrid stack according to an implementationof the disclosed subject matter.

FIG. 5 shows another example hybrid stack according to an implementationof the disclosed subject matter.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink-jet and OVJD. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processability than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, medical monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, color tunable or color temperature tunable lighting sources,heads up displays, fully transparent displays, flexible displays, laserprinters, telephones, cell phones, personal digital assistants (PDAs),laptop computers, digital cameras, camcorders, viewfinders,micro-displays, vehicles, a large area wall, theater or stadium screen,or a sign. Various control mechanisms may be used to control devicesfabricated in accordance with the present invention, including passivematrix and active matrix.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

Devices fabricated in accordance with embodiments of the presentinvention may have a plurality of electrodes, charge generation layersand/or emissive units. A preferred use of the device is in a stackedhybrid organic light emitting display, in which the shortcomings of dualunit OLED may be a limiting factor.

As used herein, “red” means having a peak wavelength in the visiblespectrum of 600-700 nm, “green” means having a peak wavelength in thevisible spectrum of 500-600 nm, “light blue” means having a peakwavelength in the visible spectrum of 470-500 nm, and “deep blue” meanshaving a peak wavelength in the visible spectrum of 400-470 nm. In someconfigurations disclosed herein where a distinction between light anddeep blue is not required, “blue” means having a peak wavelength in thevisible spectrum of 400-500 nm. Preferred ranges include a peakwavelength in the visible spectrum of 610-640 nm for red and 510-550 nmfor green.

To add more specificity to the wavelength-based definitions, “lightblue” may be further defined, in addition to having a peak wavelength inthe visible spectrum of 470-500 nm that is at least 4 nm greater thanthat of a deep blue OLED in the same device, and preferably having a CIEx-coordinate less than 0.2 and a CIE y-coordinate less than 0.5, and“deep blue” may be further defined, in addition to having a peakwavelength in the visible spectrum of 400-470 nm, as preferably having aCIE y-coordinate less than 0.15 and preferably less than 0.1, and thedifference between the two may be further defined such that the CIEcoordinates of light emitted by the third organic light emitting deviceand the CIE coordinates of light emitted by the fourth organic lightemitting device are sufficiently different that the difference in theCIE x-coordinates plus the difference in the CIE y-coordinates is atleast 0.01. As defined herein, the peak wavelength is the primarycharacteristic that defines light and deep blue, and the CIE coordinatesare preferred.

Similarly, an embodiment of the invention may include units emittingred, green, blue, and infra-red light, where an infra-red sub-pixel hasa peak emission wavelength in the range of 800-2000 nm. Such a devicemay be useful when a user wishes to avoid detection.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, medical monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, heads up displays, fully transparent displays, flexibledisplays, laser printers, telephones, cell phones, personal digitalassistants (PDAs), laptop computers, digital cameras, camcorders,viewfinders, micro-displays, vehicles, a large area wall, theater orstadium screen, or a sign. Various control mechanisms may be used tocontrol devices fabricated in accordance with the present invention,including passive matrix and active matrix.

One approach to fabricate high efficiency long-lived white OLEDs is touse a stacked hybrid architecture, in which two OLED units are separatedby a charge generation layer (CGL). One unit may be, for example, afluorescent blue unit, and the second a yellow emitting phosphorescentunit. The fluorescent blue may be chosen over a phosphorescent blue unitdue to lifetime concerns over the latter. The second unit can includeeither a single yellow emitting material or combination of red and greenemitters. However, stacked hybrid organic light emitting devicesproduced using conventional techniques may not operate at an optimalefficiency. More specifically, as a target white point for an OLED witha stacked hybrid architecture, including a fluorescent blue and aphosphorescent organic emissive unit, becomes cooler (i.e., has a coolercolor temperature) the OLED output becomes more reliant on thefluorescent blue component. Because the stacked units are notindependently controlled (i.e. the same current (density) passes througheach unit in the stack), the integrated spectral output of the device asa whole is limited by the relative efficiency of each individual unitwithin the device. As the blue spectral contribution increases, at apoint the maximum efficiency of the phosphorescent organic emissive unitcannot be used as doing so would move the spectrum away from the lessefficient blue. As a specific example, a stacked hybrid OLED may containa fluorescent blue and a second phosphorescent yellow emitting unit. Thefluorescent blue unit may have a maximum efficiency of 10% and thephosphorescent yellow may have a maximum efficiency of 20% (at the samecurrent density), resulting in a device efficiency of 30%. However, if adesired white point requires 75% (50% assumed in previous example) blueemission (e.g., three times the amount of blue emission vs.phosphorescent yellow in the resultant ‘white’ spectrum), then thepossible maximum efficiency drops to 13.3%. The 13.3% efficiency valueis a result of attributing a 10% efficiency unit to 75% of the OLEDdevice emission (i.e., the fluorescent blue unit) and then requiringonly 3.3% efficiency from the phosphorescent yellow unit i.e. from aunit that has the potential to be 20% EQE (in this example).

According to embodiments of the disclosed subject matter a secondfluorescent blue stack (i.e., at least two fluorescent blue stacks andone phosphorescent stack in total) can provide a more efficient OLED.The relative position of the three stacks may be transposed such thatthe phosphorescent stack may be placed over two blue fluorescent stacks,over a first blue fluorescent stack and under a second, or under twoblue fluorescent stacks. Notably, the efficiency for the stacked hybridOLED including at least two fluorescent blue stacks and onephosphorescent stack may be higher than that of a conventional stackedhybrid OLED. As a specific example, a stacked hybrid OLED may contain afirst fluorescent blue, a second fluorescent blue, and a phosphorescentyellow emitting unit. The first and second fluorescent blue units mayhave a maximum efficiency of 10% and the phosphorescent yellow may havea maximum efficiency of 20%, resulting in 40% device efficiency. Asshown in a previous example, a stacked hybrid OLED containing a singlefluorescent and a single phosphorescent organic emissive unit such thatthe single fluorescent organic emissive unit has to provide a largerspectral contribution to the resultant OLED spectrum than thephosphorescent organic emissive unit due to a higher blue emissionrequirement results in an OLED with lower device efficiency.Accordingly, the stacked hybrid OLED, with a cooler target white point,including at least two fluorescent blue units and one phosphorescentunit, can achieve a higher device efficiency device than a stackedhybrid OLED having only a single fluorescent blue unit.

According to embodiments of the disclosed subject matter, two or moreOLED units within a stacked structure may be separated by a chargegeneration layer. The charge generation layer may separate twofluorescent blue units or a fluorescent blue unit and a phosphorescentorganic emissive unit. A charge generation layer may be composed of ann-doped layer and a p-doped layer for injection of electors and/or holesand may be composed of any applicable material that enables injection ofelectrons and/or holes. A charge generation layer may or may not beattached to one or more electric leads and, thus, need not be directlycharged from an external electric source.

According to embodiments of the disclosed subject matter, at least onephosphorescent organic emissive unit may be included in the stackedhybrid OLED. The phosphorescent organic emissive unit may be a redorganic emissive unit, a green organic emissive unit, a yellow organicemissive unit, or a combination organic emissive unit such that theorganic emissive unit includes emitters corresponding to two or morecolors. For example, the phosphorescent organic emissive unit may be ayellow organic emissive unit. Alternatively, the phosphorescent organicemissive unit may include a combination of red and green emitters orlayers, as shown in FIG. 4 by the green emissive layer 414 and the redemissive layer 415.

FIG. 3a shows an illustrative example of an embodiment according to thedisclosed subject matter. Here, an OLED 300 may contain two electrodesand a hybrid stack between the two electrodes, as shown in FIG. 3a . TheOLED 300 may contain a first electrode 310. More specifically, the firstelectrode 310 may be a cathode or an anode and may be connected to anexternal electric source in any applicable manner such as via electricleads. A first fluorescent blue unit 312 may be disposed under the firstelectrode 310 and may emit a first blue light. A first charge generationlayer 313 may be disposed under the first fluorescent blue unit 312 anda second fluorescent blue unit 314 may be disposed under the firstcharge generation layer 312. The second fluorescent blue unit 314 mayemit a second blue light such that the first blue light and the secondblue light are within the same color region. As used herein, twoemissive units emit light in the same color region when the emittedlight from each has a peak emission wavelength within the same orwavelength range, such as where both emit light having a peak wavelengthin the “green” or “light blue” region of the visible spectrum asdisclosed herein. Similarly, the emitted light may be in different colorregions, i.e., the emissive regions emit light having peak emissionwavelengths in different color ranges as disclosed herein. For example,the first blue light may have a light blue color emission and the secondblue light may have a dark blue color emission, as disclosed herein.Alternatively, for example, the first and second blue lights may bothhave light blue color emission. A second charge generation layer 315 maybe disposed under the second fluorescent blue unit 314. A phosphorescentorganic emissive unit 316 may be disposed under the second chargegeneration layer 315 and a second electrode 318 may be disposed underthe phosphorescent organic emissive unit 316. The second electrode 318may be a cathode or an anode and may be connected to an externalelectric source in any applicable manner such as via electric leads.

FIG. 3b shows an alternative illustrative example of an embodimentaccording to the disclosed subject matter. Here, an OLED 320 may containtwo electrodes and a hybrid stack between the two electrodes, as shownin FIG. 3b . The OLED 320 may contain a first electrode 330. Morespecifically, the first electrode 330 may be a cathode or an anode andmay be connected to an external electric source in any applicable mannersuch as via electric leads. A first fluorescent blue unit 332 may bedisposed under the first electrode 330 and may emit a first blue light.A first charge generation layer 333 may be disposed under the firstfluorescent blue unit 332 and a phosphorescent organic emissive unit 334may be disposed under the first fluorescent blue unit 332. A secondcharge generation layer 335 may be disposed under the phosphorescentorganic emissive unit and a second fluorescent blue unit 336 may bedisposed under the second charge generation 335. The second fluorescentblue unit 336 may emit a second blue light such that the first bluelight and the second blue light are from the same color regionemission(s) (i.e., have the same or similar emission wavelength range)or such that they are from different color region emission(s) (i.e.,have different emission wavelength ranges). A second electrode 338 maybe disposed under the second fluorescent blue unit 336. The secondelectrode may be a cathode or an anode and may be connected to anexternal electric source in any applicable manner such as via electricleads.

FIG. 3c shows an alternative illustrative example of an embodimentaccording to the disclosed subject matter. Here, an OLED 320 may containtwo electrodes and a hybrid stack between the two electrodes, as shownin FIG. 3b . The OLED 340 may contain a first electrode 350. Morespecifically, the first electrode 350 may be a cathode or an anode andmay be connected to an external electric source in any applicable mannersuch as via electric leads. A phosphorescent organic emissive unit 352may be disposed under the first electrode. A first charge generationlayer 353 may be disposed under the phosphorescent organic emissive unit352. A first fluorescent blue unit 354 may be disposed under the firstcharge generation layer 353 and may emit a first blue light. A secondcharge generation layer 355 may be disposed under the phosphorescentorganic emissive unit and a second fluorescent blue unit 356 may bedisposed under the second charge generation 335. The second fluorescentblue unit 356 may emit a second blue light such that the first bluelight and the second blue light are from the same color regionemission(s) (i.e., have the same or similar emission wavelength range)or such that they are from different color region emission(s) (i.e.,have different emission wavelength ranges). A second electrode 358 maybe disposed under the second fluorescent blue unit 336. The secondelectrode may be a cathode or an anode and may be connected to anexternal electric source in any applicable manner such as via electricleads.

It will be understood that the configurations disclosed in accordancewith FIGS. 3a, 3b and 3c may be modified in any applicable manner. Forexample, as disclosed herein, one or more components may be added to theOLEDs disclosed in the figures, such as the various other layersdisclosed herein.

As a specific example, according to embodiments of the disclosed subjectmatter, a stacked hybrid OLED may contain a blocking layer. The blockinglayer may be disposed in any applicable location such as between aphosphorescent organic emissive layer and an electrode. The blockinglayer may act as an electron or hole blocking layer such that it impedesthe movement of electrons, holes and/or the blocking layer may carry outany other applicable function such as functioning an excition blockinglayer or the like. Alternatively or in addition, a stacked hybrid OLEDmay contain a color filter that may enable any applicable function suchas to allow one or more colors to emit from a OLED and/or a componentwithin an OLED such as an emissive unit.

According to embodiments of the disclosed subject matter, a hybridstacked OLED may include layers, as part of or external to an emissiveunit, in addition to any electrodes and charge generation layers. Theadditional layers may include an electron blocking layer, a holeblocking layer, an electron transport layer, one or more hole transportlayers, an electron injection layer, and/or a hole injection layer. Asan illustrative example, as shown in FIG. 4, an OLED may contain atransparent anode 428. A first hole injection layer (“HIL”) 426 may bedisposed over the transparent anode 428 and a first hole transport layer(“HTL”) 426 may be disposed over the first HTL 426. A first fluorescentblue unit 425 may be disposed over the first HTL 426, a first electrontransport layer (“ETL”) 424 over the first fluorescent blue unit 425,and a first charge generation layer 423 over the first ETL 424. A secondHIL 422 may be disposed over the first charge generation layer 423 and asecond HTL 421 over the second HIL 422. A second fluorescent blue unit420 may be disposed over the second HTL 421 and a second ETL 419 overthe second fluorescent blue unit 420. A second CGL 418 may be disposedover the second ETL 419 and a third HIL 417 over the second CGL 418. Athird HTL 416 may be disposed over the third HIL 417, a red emissivelayer (“EML”) 415 over the third HIL 417, a green EML 414 over the redEML 415, and a blocking layer (“BL”) over the green EML 414. A third ETL412 may be disposed over the BL 413, an electron injection layer (“EIL”)411 over the ETL 412 and a cathode 410 over the EIL 411. As anotherillustrative example, FIG. 5 shows a structure similar to that shown inFIG. 4. In the configuration shown in FIG. 5, a single yellow EML 501may be disposed over the third HTL 416, instead of the two green and redEMLs 413 and 414 as shown in FIG. 4. Various other color EMLs orcombinations of EMLs may be used. It will be understood that the stackedhybrid OLED configuration exemplified herein may be modified individualcomponents may be added, removed, and/or transposed in any applicablemanner, according to embodiments of the disclosed subject matter.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1. A device comprising: a first electrode; a second electrode; and ahybrid emissive stack disposed between the first electrode and thesecond electrode, the stack comprising: a first emissive unit thatcomprises a first fluorescent blue organic emissive unit; a first chargegeneration layer that is disposed over the first emissive unit; a secondemissive unit that comprises a second fluorescent blue organic emissiveunit that is disposed over the first charge generation layer; a secondcharge generation layer that is disposed over the second emissive unit;a third emissive unit that comprises a third fluorescent blue organicemissive unit that is disposed over the second charge generation layer;a third charge generation layer that is disposed over the third emissiveunit; and a fourth emissive unit that comprises a phosphorescent organicemissive unit that is disposed over the third charge generation layer.2. The device of claim 1, wherein the first emissive unit is disposedover the first electrode, and wherein the first electrode is an anode.3. The device of claim 1, wherein the phosphorescent organic emissiveunit of the fourth emissive unit comprises a phosphorescent greenorganic emitter.
 4. The device of claim 1, wherein the phosphorescentorganic emissive unit of the fourth emissive unit comprises aphosphorescent yellow organic emitter.
 5. The device of claim 1, whereinthe phosphorescent organic emissive unit of the fourth emissive unitcomprises a phosphorescent red organic emitter.
 6. The device of claim1, wherein the phosphorescent organic emissive unit of the fourthemissive unit comprises a phosphorescent red organic emitter and aphosphorescent green organic emitter.
 7. The device of claim 1, whereinat least one selected from the group consisting of: the first emissiveunit that comprises the first fluorescent blue organic emissive unit,the second emissive unit that comprises the second fluorescent blueorganic emissive unit, and the third emissive unit that comprises thethird fluorescent blue organic emissive unit is configured to emit bluelight in a different color region.
 8. The device of claim 1, wherein atleast one selected from the group consisting of: the first chargegeneration layer, the second charge generation layer, and the thirdcharge generation layer is comprised of at least one selected from thegroup consisting of: an n-doped layer and a p-doped layer for injectionof at least one of electrons and holes, and a material configured toenable injection of at least one of electrons and holes.
 9. The deviceof claim 1, wherein the second electrode is disposed over the fourthemissive unit, and wherein the second electrode is an anode.
 10. Thedevice of claim 1, further comprising an electron blocking layerdisposed on a side of the fourth emissive unit.
 11. The device of claim1, further comprising a hole blocking layer disposed on a side of thefourth emissive unit.
 12. The device of claim 1, further comprising: anelectron blocking layer disposed on a first side of the fourth emissiveunit; and a hole blocking layer disposed on a second side of the fourthemissive unit.
 13. The device of claim 1, wherein the hybrid emissivestack includes a color filter.
 14. The device of claim 1, furthercomprising a barrier layer disposed over the device.
 15. The device ofclaim 1, wherein the device is at least one type selected from the groupconsisting of: flat panel displays, computer monitors, medical monitors,televisions, billboards, lights for interior or exterior illuminationand/or signaling, color tunable or color temperature tunable lightingsources, heads up displays, fully transparent displays, flexibledisplays, laser printers, telephones, cell phones, personal digitalassistants (PDAs), laptop computers, digital cameras, camcorders,viewfinders, micro-displays, vehicles, a large area wall, theater orstadium screen, and a sign.